1. Field of the Invention
The present invention relates to a radiation imaging apparatus that projects radiation such as X-ray to a patient (subject) who is laying down on a tabletop of a table and a bed, and photographs with the radiation that transmits through the patient using a radiation imaging unit disposed below the tabletop, and also relates to a table for the radiation imaging apparatus.
2. Description of the Related Art
Conventionally, radiation imaging apparatuses are used in various fields such as in nondestructive inspection of a material. In this kind of radiation imaging apparatus, a so-called radiography is utilized in which an intensifying screen and a radiographic film are brought into close contact with each other. In the radiation imaging apparatus, when the radiation that transmits through the patient is incident on the intensifying screen, a phosphor included in the intensifying screen absorbs energy from the radiation and shows a fluorescence. The radiographic film is exposed to the fluorescence so that a radiological image is then recorded as a visible image.
In recent years, an image recording and reproducing apparatus equipped with a radiation detection device including a stimulable phosphor is devised. In the image recording and reproducing apparatus, when the radiation transmits through the patient and is incident on the stimulable phosphor, the stimulable phosphor stores apart of the radiation energy. When light such as visible light is radiated onto the storage phosphor, in the image recording and reproducing apparatus, the stimulable phosphor shows gleaming luminescence in accordance with the stored energy. That is, the stimulable phosphor stores radiation image information of the patient, and a scanning unit scans the storage phosphor with an excitation light such as a laser beam. Then, a signal reading unit photoelectrically reads the gleaming phosphorescence, and a recording material such as a photosensitive material or a display unit such as a CRT, records or displays the read information as the visible image.
Japanese Patent Application Laid-Open No. 08-116044 (corresponding to U.S. Pat. No. 6,075,256) discusses a radiation detection device that directly outputs digital data of the radiation in real time. The radiation digital detection device has a laminated configuration of a scintillator and a photoelectric conversion device. The scintillator converts the radiation into visible light and the photoelectric conversion device photoelectrically converts the visible light In the photoelectric conversion device, photoelectric conversion elements interposed between a transparent conducting material and an amorphous semiconductor film that includes a conducting material are arranged in a matrix on a substrate of silica glass.
Because the radiation detection device is a flat panel having a thickness of several millimeters, the radiation imaging unit that uses the radiation detection device can be easily reduced in thickness and weight. In addition, the radiation imaging unit is capable of directly obtaining a digital image without using a consumable material such as a film and a stimulable phosphor sheet. Accordingly, conventional work of mounting a cassette that stores the film or the stimulable phosphor sheet on the radiation imaging unit, is not necessary. Further, to take out the cassette in order to develop the film or the stimulable phosphor sheet after the imaging, is not necessary. Thus, a radiologist is free from complicated work.
FIG. 10 is a diagram that illustrates a conventional Bucky table that can be used to simply photograph a patient's extremities, head, and abdominal parts. In the Bucky table, a base 1 supports a tabletop 3 that allows the patient to lie down thereon via a supporting member 2. A radiation imaging unit 4 is disposed on the base 1 that is provided on an underside of the tabletop 3. In a space within the radiation imaging unit 4, the radiation detection device described above is installed. In photographing the patient laying down on the tabletop 3 on his back or on his belly, the patient is exposed to the X-ray irradiated by an X-ray tube 5 that is disposed above the patient, and the X-ray that transmits through the patient is received by the radiation imaging unit 4 so as to form the image thereof.
The radiologist needs to align a position of a part of the patient to be photographed and an image-receiving region of the radiation imaging unit 4. In order to implement the positional alignment, the Bucky imaging table includes roughly two units. One is a unit that moves the tabletop 3 in a horizontal direction so as to align the part of the patient to be photographed with the position of the image-receiving region of the radiation imaging unit 4. The other is a unit that moves the radiation imaging unit 4 so as to align the image-receiving region of the radiation imaging unit 4 with the position of the part of the patient to be photographed.
The tabletop 3 is capable of moving on the supporting member 2 for a distance L1. The radiation imaging unit 4 is capable of moving on the base 1 for a distance L2. The radiologist performs the photographing by selectively using the moving units in accordance with the circumstance and a state of the patient. However, when the radiation imaging unit 4 is moved to a leftmost position and the tabletop 3 is moved to a rightmost position at the same time, in the Bucky table as shown in FIG. 10, a left most portion of a photographing scope cannot be positioned to a close proximity of a leftmost position of the tabletop 3. That is, in photographing an extremity of the patient who is lying down, it is easy to photograph a part of the patient ranging from a cervical spine to a thigh. However, it is difficult to cover the entire extremity of the patient including the head and the leg. In addition, in the method by which both the tabletop 3 and the radiation imaging unit 4 are moved, working performance is low, and an effective photographing operation cannot be performed.
Japanese Patent Application Laid-Open No. 2003-38472 (corresponding to U.S. Pat. No. 6,934,361) discusses the radiation imaging apparatus that is capable of freely disposing the units so as to effectively operate the photographing operation. In the radiation imaging apparatus, a supporting member that supports a radiation image detection device at a position below a tabletop unit is provided to the tabletop. Thus, the radiation image detection device can be disposed and moved to a desired position over a whole part of an underside of the tabletop.
The radiation imaging apparatus disclosed in Japanese Patent Application Laid-Open No. 2003-38472 includes a detection unit that detects a first moving vector that indicates the movement of the tabletop on the base. In addition, the radiation imaging apparatus includes a moving unit that moves the radiation image detecting device in relation to the tabletop unit so that a second moving vector that indicates the movement of the radiation image detecting device in relation to the tabletop, is −1 times of the first moving vector. Thus, the photographing operation of a wide range of the patient can readily be performed.
In the conventional table, the tabletop 3 is very often slid in a widthwise direction in aligning the portion of the patient to be photographed to the position of the radiation imaging unit. FIG. 11A and FIG. 11B are diagrams that describe a positional relationship between the tabletop 3 and the radiation imaging unit 4 seen from a side of a shorter side of the tabletop 3 shown in FIG. 10, that is, from a direction of an arrow A shown in FIG. 10. Here, the tabletop 3 is supported by a tabletop frame 6. FIG. 11A shows a state in which a center of the tabletop 3 and a center of the radiation imaging unit 4 in the widthwise direction match with each other, and FIG. 11B shows a state in which the tabletop 3 is slid in a widthwise direction.
In an ordinary case, the width of the tabletop 3 in the widthwise direction is approximately 8000 mm, and the width of the radiation imaging unit 4 is approximately 5500 mm, which enables photographing by 4300 mm using 14×17 inch size film. Here, a movement amount of the tabletop 3 in the widthwise direction should be about ±150 mm. Thus, in an ordinary floating table, when the tabletop 3 is moved at a maximum, the tabletop frame 6 moves for a distance L3 so as to be positioned above the radiation imaging unit 4. In this case, the disposition of the tabletop frame 6 is as shown in FIG. 11B.
FIG. 11C is a diagram that illustrates the positional relationship in the radiation imaging apparatus that Japanese Patent Application Laid-Open No. 2003-38472 discusses. Referring to FIG. 1C, the radiation imaging unit 4 is supported by a rail 7 provided in the tabletop frame 6. Thus, the radiation imaging unit 4 can move between the rails 7.
Because of the existence of the rail 7, the tabletop 3 cannot move out of the radiation imaging unit 4. Thus, a movement amount L4 of the radiation imaging unit 4 is smaller compared to the movement amount L3 as shown in FIG. 11B. Therefore, in order to secure a sufficient movement amount, the distance between two rails 7 needs to be lengthened.
That is, as a countermeasure, the width of the tabletop 3 can be broadened. However, when the width of the tabletop 3 is broadened, a space for installation can increase. Alternatively, as a countermeasure, the radiation imaging unit 4 can go under the rail 7. However, with this configuration, the distance between the radiation imaging unit 4 and the tabletop 3 becomes longer. As described above, in the conventional examples, enlargement of the movement amount of the tabletop 3 in the widthwise direction can be restricted.
In the conventional table, when the radiation imaging unit 4 is moved in the widthwise direction, the radiologist needs to align the position of the X-ray tube 5 precisely with the center of the radiation imaging unit 4. This is because if there is a difference between a convergence position of grids used for eliminating a scattered radiation and the position of the X-ray tube 5 in the horizontal direction, an effective transmissive X-ray is cut off. In the conventional example, occurrence of the difference of the positions is prevented by adding a mechanism which moves the X-ray tube 5 according to the movement of the radiation imaging unit 4. However, while there is the X-ray tube 5 that can move according to the movement of the radiation imaging unit 4 in a lengthwise direction in a tomography etc., few X-ray tubes 5 can move according to the movement of the radiation imaging unit 4 in the widthwise direction.
In addition, as shown in FIG. 10, the radiation imaging unit 4 essentially covers the whole part of a photographing object without moving in the widthwise direction, if an image-receiving scope is enlarged. Thus, a mechanism for moving the radiation imaging unit 4 in the widthwise direction is not required. However, when the radiation imaging unit 4 is supported by the tabletop 3, in terms of structure, a mechanism for moving the radiation imaging unit 4 in the widthwise direction is necessary. For example, the tabletop 3 can be moved instead of moving the radiation imaging unit 4 so as to align the radiation imaging unit 4 with the position of the photographing portions of the patient. However, in this method, when the tabletop 3 is moved in the widthwise direction, the radiation imaging unit 4 has to be moved back to an original position in the same movement amount as the tabletop 3.
In addition, in the conventional table, when the radiation imaging unit 4 and a supporting member that supports the radiation imaging unit 4 are provided in the moving tabletop 3, a gross mass of the tabletop 3 and an inertial force of the tabletop 3 increase. Accordingly, a force required for moving at the time of operation by the radiologist, and a sway of the imaging table at the time of stopping the moving operation increase, and thus operability can deteriorate. Especially, the sway that occurs at the time of stopping the movement in the widthwise direction, causes also the body of the patient to sway so that the patient feels unnecessary pain.
As described above, the conventional table is good in the operability of the tabletop 3 in the lengthwise direction, but there is a defect with respect to the operability of the tabletop 3 in the widthwise direction.
In addition, in moving the tabletop 3 on a horizontal plane, a sufficient space is necessary around the apparatus in accordance with the movement amount of the tabletop 3. However, in actual use, instruments such as a drip infusion stand and a monitoring device for the patient are placed around the table. Accordingly, the movement range of the tabletop 3 in the widthwise direction can be restricted. In this case, the radiologist is required to deliberately perform the operation while confirming the surrounding state, and thus the operability deteriorates.